I. Field of the Invention
This invention relates generally to respiration monitoring apparatus, and more particularly to a face mask mounted pneumotachograph that obviates the need for the wearer to insert the pneumotachograph in his/her mouth as inspiratory and expiratory gas flows are being measured.
II. Discussion of the Prior Art
In the Howard U.S. Pat. No. 5,363,857, assigned to AeroSport, Inc., there is described a metabolic rate analyzer that measures flow, O2 consumption and CO2 production and provides a readout of a test subject""s respiratory performance obtained during the course of an exercise regimen. In the system described, the test subject is made to breath in and out through a mouthpiece as differing levels of work are performed on a treadmill or stationary bicycle.
The Norlien et al. U.S. Pat. No. 5,038,773, also assigned to applicants"" assignee, describes a respiratory gas flow measuring and indicating system that incorporates a tubular, molded plastic, open-ended structure in the lumen of which is provided a pair of molded ribs which intersect to form a cross. The ribs are also tubular and each includes a series of minute apertures and opposed sides thereof which act as pitot tubes. As is described in the ""773 patent, the invention of that patent offers significant advantages over known pneumotachograph devices. For example, because the mouthpiece of the flow meter system of the ""773 patent has a very low dead space, gas analyzers incorporated in the system are not adversely affected by the rebreathing of previously expired, CO2 rich air. However, with a mouthpiece that is designed to be held in the mouth between the lips of the subject, swallowing becomes somewhat more difficult and there is a tendency to gather saliva in the mouth, especially in subject""s undergoing heavy exercise. Saliva can collect on the cruciform ribs of the pneumotachograph and occlude the apertures comprising the pitot tube structure, thus resulting in inaccurate gas flow measurements. Thus, it would be advantageous to have a respiratory gas flow measurement sensor that need not be inserted in the test subject""s mouth. The Rudolph U.S. Pat. No. 5,265,595, assigned to Hans Rudolph, Inc., describes a face mask structure designed to support a pneumotachograph in close proximity to, but not in, the test subject""s mouth. The particular mask design reflected in the ""595 patent purports to provide a low dead space between the subject""s face and the portion of the mask that is designed to encircle and cover the subject""s mouth.
As is set out in a subsequent Rudolph et al. U.S. Pat. No. 6,082,360, the device described in the Rudolph ""595 patent suffers from a serious defect, namely, the mask of the ""595 patent leaks air around the periphery of the mask when being worn by a user which allows escape of expired gases from the mask or drawing outside air into the mask other than through the pneumotachograph. The solution set forth in the Rudolph ""360 patent is to apply a sticky, moist hydrogel seal between the patient""s skin and the mask in an effort to cure the leakage problem. It has been reported that many subjects consider the application and subsequent removal of the sticky, moist seal to be somewhat unpleasant.
A need, therefore, exists for a face mask that (1) incorporates a respiratory flow sensor that substantially eliminates any dead space between the wearer""s face and the flow sensor and which also seals tightly against the face of the wearer to prevent air leakage; (2) is sufficiently low cost so as to allow single patient use in a clinical setting and yet be launderable in those applications where the respiratory measurements are being made in a health club setting; and (3) that reduces anxiety and stress by being comfortable and effective allowing normal work to continue.
The foregoing advantages are achieved by providing a respiratory monitor apparatus that has a mask adapted to be secured to the face of a person so as to enclose the nose and mouth where the mask is formed from a soft, conformable, gas-impermeable elastic fabric allowing it to conform to the person""s face with substantially zero air space therebetween. The elastic fabric has at least one aperture of a predetermined size and shape extending through its thickness dimension incorporating a soft rubber grommet. A respiratory flow sensor is mounted within the grommet and is of a size and shape to exhibit a zero clearance fit with a portion of the mask defining the aperture.
The elastic fabric is preferably spandex, formed from woven Lycra(copyright) fibers and to provide more rigid support for the flow sensor, the spandex fabric may be laminated with neoprene sponge rubber of a predetermined thickness.